INSTRUCTION DESCRIPTIONS
A - 228 INSTRUCTION SET DETAILS MOTOROLA
Operation: Assembler Syntax:
±S1∗S2 ➞ D (parallel move) MPY (±)S1,S2,D (parallel move)
±S1∗S2 ➞ D (parallel move) MPY (±)S2,S1,D (parallel move)
±(S1∗2-n)➞D (no parallel move) MPY (±)S,#n,D (no parallel move)
Description: Multiply the two signed 24-bit source operands S1 and S2 and store the
resulting product in the specified 56-bit destination accumulator D. Or, multiply the
signed 24-bit source operand S by the positive 24-bit immediate operand 2-n and add/
subtract to/from the specified 56-bit destination accumulator D. The “–” sign option is
used to negate the specified product prior to accumulation. The default sign option is “+”.
Note: When the processor is in the Double Precision Multiply Mode, the following
instructions do not execute in the normal way and should only be used as part of the
double precision multiply algorithm shown in Section 3.4 DOUBLE PRECISION MULTI-
PLY MODE:
MPY Y0, X0, A MPY Y0, X0, B
MAC X1, Y0, A MAC X1, Y0, B
MAC X0, Y1, A MAC X0, Y1, B
MAC Y1, X1, A MAC Y1, X1, B
All other Data ALU instructions are executed as NOP’s when the processor is in the Dou-
ble Precision Multiply Mode.
Example 1: :
MPY –X1,Y1,A #$543210,Y0 ;–(X1∗Y1) ➞ A, update Y0
:
MPY Signed Multiply
MPY
Before Execution After Execution
X1 $800000
Y1 Y1
$C00000 $C00000
$800000
X1
A$00:000000:000000 $FF:C00000:000000
A